Titanium dioxide (i.e., TiO2 or titania) is a multi-functional material that has attracted extensive research and development efforts in the last two decades. It has applications in energy and environmental fields in addition to its traditional usage as a white pigment. Some applications of TiO2 include gas sensors, electrochromic devices, dye-sensitized solar cells, and photocatalysts.
Various photocatalysts have been developed using TiO2 and applied to fields such as air/water purification, self-cleaning, anti-fogging (hydrophilic/hydrophobic switching), sterilization, and hydrogen production through water-splitting. Two properties of TiO2 that influence its application are its crystal structure and surface morphology. Usually, a “nanocrystalline” structure is ideal for TiO2 films to achieve high functional performance. This is because i) the high specific surface area provides superior surface activity when the particles are of nanometer-scale dimensions; and ii) catalytic activity is sensitively associated with the crystallinity of individual nanoparticles, and good crystallinity (in anatase, brookite, or rutile structures) is generally desired.
Known methods for depositing TiO2 films include various vacuum deposition techniques (e.g., physical vapor deposition (PVD), chemical vapor deposition (CVD), pulsed laser deposition (PLD), and sputtering), and solvent or aqueous-based methods in which titanium dioxide dispersions are coated and then dried. The vacuum deposition techniques require expensive specialized equipment that is typically not well-suited for preparing thick coatings at a high production rate. In contrast, liquid based coating methods require energy to remove the liquid and may result in coatings having impurities that adversely affect properties (e.g., photocatalytic properties) of the TiO2 layer.